Proper disposal of solid waste has become an increasingly serious problem as existing sites for land disposal near capacity and new sites become increasingly difficult to locate. Incineration of combustible solid waste has long been used to reduce the quantity of solid matter needing disposal.
Watercooled rotary combustors have been developed to burn solid waste efficiently and economically. The heat energy which results from the burning of the solid waste is used to produce steam for use in generating electricity or for other industrial process uses. Various watercooled rotary combustors are described in U.S. Pat. Nos. 4,735,157 (Jurusz), which issued Apr. 5, 1988, 4,226,584 (Ishikawa), which issued Oct. 7, 1980, 4,066,024 (O'Connor), which issued Jan. 3, 1978, 3,822,651 (Harris et al.), which issued July 9, 1974, and 518,285 (Storer), which issued Apr. 17, 1894.
U.S. Pat. Nos. 3,822,651 (Harris et al.) and 4,735,157 (Jurusz) disclose a rotary kiln and combustor, respectively, each formed by a plurality of pipes joined to define an inner cylindrical surface and being interconnected to permit water flow through the pipes. During operation, burnable waste is dumped into one end of the rotary combustor. The combustor rotates and the burning waste slowly tumbles downwardly forming a kind of spiraling fire bed until what has not been consumed spills into the boiler.
Each of the aforementioned watercooled rotary combustors is designed with a cylindrical water tube cooled (membrane wall) combustor. (See FIG. 3 attached hereto). These combustors are fabricated of cylindrically welded walls consisting of water tubes and flat bars, i.e., the flat bars are disposed between and welded to adjoining tubes. The cylindrical welded wall is then welded into headers at each end. These cylindrical watercooled rotary combustors are installed having a downward slope towards the boiler.
During operation these combustors rotate at very slow speeds. The rotation and tilted axis convey the refuse or solid waste through the combustor and facilitates the mixing of the refuse during combustion. The bars (fins) of the membrane wall include perforations to admit forced draft combustion air. The combustion air is typically pre-heated and penetrates the burning refuse material.
Typically, refuse is fed into a cylindrical watercooled rotary combustor via a hopper at the upper inclined end and a hydraulically actuated ram-type feed system places the refuse into the combustor. The partially burned refuse, ash, and gases leave the combustor at the lower outlet end and into a boiler where completion of the combustion takes place in the radiant section of the boiler.
Combustion in an incinerator or combustor is greatly dependent upon maintenance of a continuous supply of air, i.e., oxygen, to support the burning reaction, and fast, complete combustion requires not only an adequate supply of air but also good mixing or distribution of the air through the desired combustion region.
The need for proper air flow is exemplified in U.S. Pat. No. 4,226,584 (Ishikawa). The Ishikawa patent discloses a rotary kiln similar to that set forth in U.S. Pat. No. 3,822,651. In an attempt to overcome restriction to the air flow within the kiln, a plurality of pins, secured directly to the pipes on the inside of the cylinder, were provided to create a pattern of projections to support burning material slightly spaced from the inner cylinder wall. The pins prevent air flow blockage and also increase the effective distribution of air under and through the combustion zone.
Although the pin design of the Ishikawa patent may aid in preventing blockage to the air flow in the combustor, it is extremely costly and time consuming to affix pins to the walls of each tube. Furthermore, the manufacturing techniques required in fabricating cylindrically shaped combustors is also expensive and extremely labor intensive.
The present inventor has designed a novel multi-sided watercooled rotary combustor which avoids the increased manufacturing costs associated with a cylindrical watercooled combustor, while improving the mixing action of the refuse by causing an increase in the tumbling and agitation of the refuse. The multi-sided design is fabricated from membrane wall tube panels. These membrane wall tube panels can be manufactured with readily available automatic equipment.
The increased tumbling and agitation provided by the multi-sided design according to the present invention improves drying of the refuse and promotes better combustion efficiency. The breaking-up of the refuse by the increased tumbling and agitation results in clinker reduction. The improved mixing and agitation also reduces the need for pre-heated combustion air and minimizes clogging of the air ports.
Thus, the novel combustor design of the present invention results in substantial economic benefits due to its improved combustion efficiency, clinker reduction, reduced pre-heated combustion air requirements and reduced clogging of air ports. Furthermore, the combustor requires less maintenance which results in less down time and increased operation.
Finally, the multi-sided combustor design avoids the need for circular headers which facilitates every phase of header fabrication and eliminates all fabricating operations associated with bending of the header pipe.
Additional advantages of the present invention shall become apparent as described below.